In July there was a 50 per cent increase in the number of emails containing malicious files.
According to Kaspersky Lab, despite a noted downturn in spam, these emails accounted for 4.4 per cent of all mail traffic in July, despite there being an average of 74.3 per cent of spam in the second quarter of 2012.
Maria Namestnikova, senior spam analyst at Kaspersky Lab, said: “On top of the 4.4 per cent of email traffic containing malicious attachments, there was also spam that contains malicious links and fraudulent messages.
“August looks like it could be the peak month for dangerous spam. In the final summer month last year the share of malicious attachments almost reached six per cent. Everything points to a repeat of that spike in malicious code this August.”
Symantec's Intelligence Report for July 2012 detected spam at a level of 67.6 per cent, and pointed to the takedown of the Grum botnet as a possible reason for the downturn.
It said that the most common spam category in July was related to newsletters, with 57 per cent of spam in this format, a move from 0.08 per cent of spam in June. Symantec deemed this likely to be the result of a campaign by the Festi botnet that used the social engineering tactic of spoofing newsletters quite heavily in July.
The average spam message size in July was between 0Kb – 5Kb, accounting for 4,707 per cent of all spam seen.
Namestnikova said she expected a gradual decline in the proportion of spam, which could drop to the 65 per cent mark of total mail traffic within the next year.